Field of the Invention
The invention relates to borehole logging devices and more particularly to caliper tools for determining profiles of boreholes.
There is a need to determine profiles in various kinds of boreholes such as geothermal boreholes because irregular shaped and sized casings occur, rocks fall from one side of the hole, casings split, fractures occur and other events happen within the hole making periodic monitoring of the borehole advisable. Fracture orientation can be determined by utilizing three or more independent arms in accordance with the invention.
There exists a need for a reliable caliper tool which is operable at the high temperatures encountered in geothermal wells, i.e. on the order of about 250.degree. C.
It is desirable that a caliper tool be accurate and that it can be raised and lowered repeatedly in the same downhole run.
In addition, the caliper and contour tool of the invention may be utilized to determine fracture orientation, shape and size in boreholes and can be utilized to determine the best place to set packers, cement, kick off and the like. Basically, tools of this nature are lowered to a point below the depth desired to be monitored and the arms are extended. The tool then is withdrawn at a preselected rate which can be either fast or slow. Calipers monitor contact with the walls of the hole and electrical signals are produced in accordance with their extension. The signals are monitored at the surface and a determination is made of the borehole's contour or profile. A tool may be repeatedly lowered and raised to obtain a plurality of readings to get a very complete picture of the borehole. There are devices well known in the art such as photographic compasses utilized to record North at various time intervals to determine the disposition of the arms within the borehole as well as inclinometers and magnetometers for determining the orientation of the tool within the hole so that an accurate three dimensional profile of the borehole is obtainable. Many other uses for borehole logging devices are well known to those skilled in the art and there is no need to explore them further herein.